首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1191篇
  免费   59篇
  国内免费   2篇
林业   135篇
农学   88篇
基础科学   15篇
  291篇
综合类   85篇
农作物   105篇
水产渔业   91篇
畜牧兽医   308篇
园艺   18篇
植物保护   116篇
  2023年   8篇
  2022年   32篇
  2021年   34篇
  2020年   36篇
  2019年   34篇
  2018年   46篇
  2017年   53篇
  2016年   42篇
  2015年   29篇
  2014年   47篇
  2013年   111篇
  2012年   69篇
  2011年   77篇
  2010年   62篇
  2009年   52篇
  2008年   56篇
  2007年   24篇
  2006年   40篇
  2005年   24篇
  2004年   24篇
  2003年   33篇
  2002年   32篇
  2001年   35篇
  2000年   23篇
  1999年   20篇
  1998年   10篇
  1997年   14篇
  1996年   14篇
  1995年   4篇
  1990年   7篇
  1989年   5篇
  1988年   11篇
  1987年   9篇
  1986年   5篇
  1985年   4篇
  1984年   5篇
  1983年   8篇
  1981年   8篇
  1980年   8篇
  1979年   8篇
  1978年   4篇
  1977年   8篇
  1976年   6篇
  1975年   7篇
  1973年   9篇
  1972年   4篇
  1971年   6篇
  1970年   6篇
  1969年   7篇
  1968年   7篇
排序方式: 共有1252条查询结果,搜索用时 45 毫秒
951.
952.
In a pot experiment using a strongly P‐fixing Andosol from Nicaragua, the effects of sugarcane–filter cake application on the growth of white mustard (Sinapis alba L.) were compared with those of 13C‐labeled pea residues. The application of pea residues led to a 50% increase and the application of filter cake to a 30% decrease in soil organic matter–derived microbial biomass C compared with the control. In contrast, the application of filter cake resulted in a four times higher content of substrate‐derived microbial biomass C than that of pea residues. The application of organic substrates generally increased microbial biomass N. Mustard growth led to significant increases in microbial biomass P in the control, but also in the organic‐amendment treatments, which always resulted in decreased microbial biomass C : P ratios. Mustard growth also led to increased contents of Bray‐1‐extractable P, but this increase was only significant in the filter cake treatment. The application of pea residues had no effect on the yield of shoot C, but a positive effect on the yield of root C in comparison with the nonamended control. In contrast, the application of filter cake significantly depressed yields of shoot C and root C, due to N immobilization, presumably due to the high concentration of lignin.  相似文献   
953.
Abstract

Seasonal incidence of shootfly, Atherigona naqvii Steyskal was studied in wheat sown on nine dates at approximately fortnightly intervals from 1 October to end of January during the 1973–74 to 1976–77 seasons at Jaipur, India. During the season the pest remained more active from the second fortnight of October to mid-December and again during February and March. These fluctuations appear to have a positive correlation with maximum and minimum temperatures while relative humidity and rainfall did not have any influence. The winter low temperatures during mid-December to mid-February arrested the flies' activity. The crop sown between mid-November and mid-December was found to be almost free from shootfly and no control measures are needed. However, early and late sown crops remained prone to attack.  相似文献   
954.
The objectives of the experiment were to determine the effect of two doses of equine chorionic gonadotropin (eCG) in a standard synchronization protocol based on a short-term progesterone (P4) priming on ovarian structures and haemodynamics, concentrations of steroid hormones and prolificacy rate when oestrus was induced during low-breeding season (LBS) in Beetal dairy goats. We hypothesized that inclusion of eCG in a short-term P4 priming-based synchronization protocol would increase the blood perfusion to ovarian structures leading to enhance oestrous and ovulatory responses and prolificacy rate in goats. Forty-two multiparous acyclic goats were blocked by body condition and, within block, assigned randomly to receive saline as control (CON), low eCG (L-eCG; 300 IU) or high eCG (H-eCG; 600 IU) dose. Initially, a controlled internal drug release (CIDR) device was placed in the anterior vagina on d −8, followed by removal of CIDR on d −3, concurrent with the administration of PGF and eCG according to their respective treatments. Goats were monitored for oestrous response. B-mode and Doppler ultrasonography was performed with 12-h interval, starting from day −3 until natural breeding (day 0), and then on days 5, 10, 15 and 20 post-breeding to monitor follicular and luteal dynamics and blood flow, respectively. Blood was sampled at 0, 12, 24, 36 and 60 h after CIDR removal to quantify plasma concentrations of estradiol-17β (E2), whereas plasma concentrations of P4 were assayed at days 5, 10, 15 and 20 after breeding. Pregnancy and prolificacy rates were determined at day 30 and 150 after breeding, respectively. Data were analysed with mixed-effects models, and orthogonal contrasts were used to evaluate the effect of treatment [Con vs. (½ L-eCG + ½ H-eCG)] and dose of eCG (L-eCG vs. H-eCG). Data are presented in sequence as CON, L-eCG, H-eCG (LSM ± SEM). The oestrous intensity score (152.9 vs. 182.7 vs. 186.5 ± 15.1; p = .02) was greater in eCG-treated goats as compared to CON. Administration of eCG reduced the intervals to standing oestrus (66.2 vs. 41.8 vs. 48.9 h ± 5.5; p = .05), breeding (70.2 vs. 44.4 vs. 45.4 h ± 4.5; p = .03) and ovulation (84.5 vs. 61.2 vs. 63.4 h ± 6.2; p = .05) compared with CON goats. The mean growth rate of pre-ovulatory follicle was greater (1.11 vs. 1.49 vs. 1.45 mm ± 0.08; p = .01) in eCG-treated goats resulting in an increased diameter of pre-ovulatory follicle (6.27 vs. 7.20 vs. 7.31 mm ± 0.07; p < .01) and corpora lutea (6.75 vs. 8.26 vs. 8.07 mm ± 0.42; p = .04) than CON. The mean follicular blood flow did not differ among treatments; however, the mean luteal blood flow was greater in L-eCG-treated goats (0.81 vs. 1.61 vs. 1.07 cm2 ± 0.12; p = .001). The mean concentrations of E2 (4.03 vs. 5.21 vs. 4.78 pg/ml ± 0.42; p = .04) and P4 (4.85 vs. 6.39 vs. 6.22 ng/ml ± 0.34; p = .04) were greater in eCG-treated goats. The twinning rate did not differ between treatments; nevertheless, prolificacy rate was greater (p = .04) in L-eCG-treated goats. Collectively, our data suggest that the administration of eCG improves the induction of oestrous and ovarian dynamics. Administration of L-eCG enhances prolificacy rate, therefore, a low dose of eCG might be practically beneficial to improve reproduction during LBS in acyclic Beetal dairy goats.  相似文献   
955.
956.
The selenium status of three different classes of goats ((i) female lactating, (ii) female non-lactating, and (iii) male goats) grazing semi-arid pasture in the southern part of the Punjab province, Pakistan and that of selenium concentration of soil and dietary sources, ingested by those animals were investigated during two different seasons of the year (winter and summer). Soil, forage, feed, water from the pasture and blood plasma, urine, faeces, and (if applicable) milk from these goats were collected fortnightly. The samples were analyzed for selenium concentrations. Soil selenium showed both seasonal and sampling periods effect on its concentration while forage selenium was affected only by the seasonal changes. No significant effect of seasons or fortnights on feed selenium level was observed. In fecal samples selenium concentration in lactating and non-lactating and plasma of male goats were affected by sampling periods. While fecal selenium in male goats showed significant effect on its concentration both seasonal and within fortnights. Severe deficient level of soil selenium during both seasons and marginal deficient level of forage selenium during summer were observed. Selenium concentrations in feed slightly exceeded the requirements of ruminants in feed during both seasons of the year. Plasma selenium concentrations in all goat classes were higher in winter than that in summer showing no seasonal or fortnight variation and its concentration was slightly lower in lactating goats as compared to other classes. On the bases of these results, it is concluded that overall selenium status of the goats based on plasma selenium concentration may be considered adequate mainly due to the mineral supplement provided all over the year, since soil and forage selenium concentrations were low to deficient.  相似文献   
957.
OBJECTIVE: To describe the clinical signs following ingestion of an herbal supplement containing guarana and ma huang in dogs, estimate minimum dose at which clinical signs of toxicosis and death were reported, and evaluate treatment options. DESIGN: Retrospective study. ANIMALS: 47 dogs with evidence of ingestion of an herbal supplement containing primarily guarana and ma huang. PROCEDURE: Records of dogs that had ingested an herbal supplement containing ma huang and guarana between July 1997 and October 1999 were retrieved from the National Animal Poison Control Center database. Data were retrieved and reviewed regarding signalment, dose ingested, clinical signs, laboratory test results, treatment, and final outcome. Cases were assessed by staff veterinarians as toxicosis or suspected toxicosis on the basis of strength of evidence supporting a diagnosis. RESULTS: Most dogs (80%) developed clinical signs of toxicosis within 8 hours of ingestion, and clinical signs persisted for up to 48 hours. Hyperactivity, tremors, seizures, and behavior changes were reported in 83% of dogs; other signs included vomiting (47%), tachycardia (30%), and hyperthermia (28%). Seventeen percent of the dogs died or were euthanatized. Estimated doses of guarana and ma huang ranged from 4.4 to 296.2 mg/kg (1.98 to 133.2 mg/lb) and 1.3 to 88.9 mg/kg (0.58 to 40.0 mg/lb) of body weight, respectively; minimum dose at which death was reported was 19.1 mg of guarana/kg (8.7 mg/lb) and 5.8 mg of ma huang/kg (2.6 mg/lb). CONCLUSIONS AND CLINICAL RELEVANCE: Accidental ingestion of herbal supplements containing primarily guarana and ma huang in dogs can lead to a potentially lethal condition that may require prompt detoxification and supportive treatment for several days. Most dogs recovered with supportive treatment.  相似文献   
958.
Opium poppy (Papaver somniferum L.), an important medicinal plant, produces several opiate alkaloids including morphine, thebaine, codeine, papaverine and noscapine. Polysaccharides, such as sodium alginate, have been used in depolymerized form as wonderful promoters of plant growth. The present study has revealed that application of alginate oligosaccharides (AO), obtained from sodium alginate irradiated by Co-60 gamma rays, significantly enhances certain physiological/biochemical parameters as well as the overall growth of opium poppy. The highest dose applied was the most effective in increasing the morphine and codeine contents as well as the overall yield of crude opium per plant.  相似文献   
959.
Various serological tests were used for the diagnosis of glanders in the past but still complement fixation test (CFT) is the internationally prescribed test for trading equines. A new immunoblot (IB) technique has recently been introduced to overcome the well known shortcomings of CFT i. e. a considerable number of false positive and negative results and anticomplementary effects of sera. The objective of this study was the comparative evaluation of two glanders CFT antigens commercially available at Central Veterinary Institute ofWageningen UR, Lelystad, NL (CIDC) and at c.c.pro GmbH, Oberdorla, DE (c.c.pro) in a glanders endemic area regarding specificity and sensitivity. A total of 1678 serum samples from the endemic region (Province Punjab, Pakistan) and a non-endemic area (Germany) were analysed. All sera tested positive or suspicious with CFT were analysed by the confirmatory IB to exclude CFT false positive results. Both CFT antigens showed 100% sensitivity. The use of CIDC or c.c.pro antigen resulted in specificities of 77.45% or 75.71% for sera from endemic area and 93.75% or 94.79% for sera from non-endemic areas, respectively. The results demonstrate the different performances of identical tests in different epidemiologically settings. Based on these results, the combined use of CFT and IB is highly suggestive for the serodiagnosis of glanders. Good agreement was calculated between CFT (using either c.c.pro or CIDC antigen) and immunoblot.  相似文献   
960.
A field experiment was conducted to study the impact of tillage, crop residue management and nitrogen (N) splitting on spring wheat (Triticum aestivum L.) yield over 2 yr (2010-2012) in a rice (Oryza sativa L.)-wheat system in northwestern Pakistan. The experiment was conducted as split plot arranged in randomized complete blocks design with three replications. Treatments comprised six tillage and residue managements: zero tillage straw retained (ZTsr), zero tillage straw burnt (ZTsb), reduced tillage straw incorporated (RTsi), reduced tillage straw burnt (RTsb), conventional tillage straw incorporated (CTsi), and conventional tillage straw burnt (CTsb) as main plots and N (200 kg ha−1) was applied as split form viz., control (no nitrogen & no splitting, N0S0); 2 splits of total N, half at sowing and half at the 1st irrigation (i.e., 20 d after sowing (DAS)) (NS1); 3 splits of total N, 1/3 at sowing, 1/3 at the 1st irrigation, and 1/3 at the 2nd irrigation (NS2); 4 splits of total N, 1/4 at sowing, 1/4 at the 1st irrigation, 1/4 at the 2nd irrigation (45 DAS), and 1/4 at the 3rd irrigation (70 DAS) (NS3); and 4 splits of total N, 1/4 at the 1st irrigation, 1/4 at the 2nd irrigation, 1/4 at the 3rd irrigation, and 1/4 at the 4th irrigation (95DAS) (NS4) as sub plots. The results showed that the most pikes m−2, grains/spike, 1000-grain weight, grain yield, and N use efficiency (NUE) were obtained at zero tillage, straw retained and 4 splits application of total N (i.e., at sowing 20, 45 and 70 d after sowing). The results indicated that ZTsr with application of 200 kg N ha−1 in 4 equal splits viz. at sowing 20, 45 and 70 d after sowing is an appropriate strategy that enhanced wheat yield (7436-7634 kg ha−1) and N efficiency (28.6-29.5 kg kg−1) in rice-wheat system.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号